Her original dress is mainly white with a lot of blood, but becomes completely red, then white with a lot of blood again when she runs out of the house.
Samantha's hair changes from almost straight to very curly when she is at the house, babysitting.
When Sam turns on the lightbulb on the stairs to the attic, she causes a short circuit, so every light in the house goes out. When she's swooning, the hallway is at least lit by moonlight, even so there is an eclipse.
The TV newscaster claims that the eclipse of the moon will become total around midnight and "that's when you'll actually be able to see the moon itself disappear." However, due to the refracting effects of earth's atmosphere, the moon does not "disappear" at all during an eclipse, even when completely in the earth's shadow, but only becomes orange/red. (An actual image of the moon in full eclipse is in fact shown - in several, quick flashes - later in the film.)
When Samantha grabs the pizza, she holds the box vertically. This would cause the pizza to "collapse" inside the box. However, when she opens the box, the pizza is flat. Also, it appears as though a piece of the pizza is missing. However, what appears to be a missing piece is actually a part of the pizza that had shifted and collapsed when she held the box up
When Samantha is trying to escape near the end of the film, she slips and falls into several pools of blood. But when she gets up & runs up the stairs, she leaves no bloody footprints behind.
When Samantha drops the phone receiver both at the pay phone outside the college and in the Ulman's kitchen, the sound is not the dial tone that would immediately follow a hang up on a land line, but a tone that occurred after the phone had been off the hook for more than five minutes.
When Samantha and Megan are first driving to the house for the babysitting job, they drive down a single lane road with no stops. Megan stares almost continuously at Samantha and talks, yet the car never shifts to the right or left whatsoever. A closer look at the wheel reveals that it is completely stationary.
When Samantha is waiting at her campus a car alarm is clearly heard going off. Cars did not have those type of alarms in 1983.
The Connecticut license plates used in the film were not issued until 2000. In the 80s, when the film is set, passenger cars would generally have plates with white letters/numbers on a solid blue background, not the "blue fade" design currently in use and shown in the film.
The film is based on a location in Connectict in the 80's, however in the beginning when she calls about the babysitter job she uses a quarter in the payphone. Connecticut did not raise payphone rates from 10 cents to 25 cents until 1997 shortly before Vermont.
At about 11 minutes in, as Samantha is walking up to a building with large pillars, a few more modern cars can be seen driving past in the background.
The film is set in the 1980s, yet in an around Samantha's dorm there are modern outdoor lights, garbage cans, and faucets.
The rotary phone inside the house has a "516" area code, which is Nassau County, Long Island, NY. There is also an emergency sticker on the phone displaying the real life working phone number for the New Hyde Park Fire Department. New Hyde Park is a suburb on Long Island, NY. However, the film is set in a remote area on the outskirts of an upstate college town.
When Samantha is holding the knife near the bottom of the stairs, she says, "Mrs. Ulman?" referring to Mr. Ulman's mother-in-law. Her last name would most likely not be the same as her son-in-law's last name.